Systems are known and in commercial use in which there are provided, at various locations, a plurality of sensing means for sensing conditions at those locations, and a plurality of control means for controlling these conditions. The sensors and the control means are typically connected to so-called "controllers", usually one at each of the locations and each usually having its own microprocessor. The controllers in turn are connected, for example over two-wire lines, to a programmer station containing a computer, where the signals from the controllers are processed and, typically, displayed; signals are also sent from the computer to the controllers for controlling the control means at the various locations.
It is also known to provide on the monitor of the programmer station a plurality of programming "window" displays selectable by an electrical "mouse" or by manipulation of a keyboard, each displaying its information in a different window. For example, pursuant to the IEC 1131-3 Standard, four languages may be displayed, namely Ladder Logic Diagram, Function Block Diagram, Structured Text and Sequential Function Chart (SFC), the natures of which are set forth hereinafter. One of these, the Sequential Function Chart or SFC, is similar to a flow diagram in that it displays the sequence of steps to be performed by the program. These languages may be used in establishing programs for running the controllers and, by using mouse and/or keyboard, each display and the corresponding program can be monitored, edited and changed as desired.
The present invention is primarily concerned with a portion of the system comprising a control system which permits an operator to monitor, edit and/or change the Sequential Function Chart which corresponds to the program for a selected controller microprocessor. However, while the IEC 1131-3 Standard provides for and specifies the nature of the SFC language, it does not offer any suggestion as to how a Chart may conveniently be monitored, edited and/or changed.
More particularly with regard to the history of the prior art, many industrial processes can be automatically controlled by computing equipment that receives the results of sensor equipment, calculates results, and generates signals to actuating devices. The earliest versions of such equipment typically included meters and gauges so that a human could observe sensor and controller signals. The early equipment also typically included dials and switches so that a human could establish desired operating points and operating modes. As computing technology became available, the control functions were distributed between many computing devices. Certain computing devices were created specifically to perform high speed control calculation functions. Other computing devices were created to perform human interface functions. Still other computer devices were created to perform other specialized functions such as data recording, alarm detection, etc. This latter type of industrial control system is generally known as a "Distributed Control System" (DCS).
Computing devices of the DCS type are typically general purpose devices capable of performing a number of different control calculations. The exact nature of the control calculation is established by each individual user via a variety of different mechanisms, generally computer programs. Some manufacturers use data tables entered by the user to establish the control calculations. Many other methods are also used to establish the control calculations.
An effort to standardize the method used to establish control calculations began several years ago. The result of this effort is the Standard 1131-3 of the International Electrotechnical Commission (IEC) referred to above. This standard specifies the five different methods or program languages mentioned above, namely Function Block, Ladder Diagram, Structured Text, Instruction List, and Sequential Function Chart. A control computer that permits use of any selectable one of these languages, i.e. Function Block, Ladder Diagram, Sequential Function Chart and Structured Text to establish control calculations was introduced by Moore Products Co. of Springhouse, Pa. in 1992. A Product Information bulletin PI39-3, Issue 1, published in March of 1993 by Moore Products Co. describes such a distributed control system permitting use of any of these four methods or languages, and is included in this specification at its end as Appendix I. This is also described in an article entitled "A DCS-PLC COMBINATION PUTS FUNCTIONS INTO MODULES" appearing in the August 1992 issue of "Control Engineering" and comprising Appendix II of this specification.
The Sequential Function Chart (SFC) method or language is a means to describe a sequence of program actions and steps graphically. The graphical representation of the sequence reduces the engineering time to develop, enter, trouble shoot and maintain a sequential process control strategy. SFC's are typically used in batch chemical and pharmaceutical applications and for the control of discrete parts manufacturing equipment, although they may be used for many other purposes as well.
The 1131-3 standard for the Sequential Function Chart method does not provide any particular means for an operator to control exactly how the SFC functions; however, how it functions can be important depending on the situation, for example, to meet the needs of an operator of a chemical process or manufacturing machine, and permit the operator to assume control of the execution of one or more SFC's so as to monitor, edit or change the corresponding program.